105 research outputs found
Formation of Primordial Stars in a LCDM Universe
We study the formation of the first generation of stars in the standard cold
dark matter model, using a very high-resolution hydordynamic simulations. Our
simulation achieves a dynamic range of 10^{10} in length scale. With accurate
treatment of atomic and molecular physics, it allows us to study the
chemo-thermal evolution of primordial gas clouds to densities up to n =
10^{16}/cc without assuming any a priori equation of state; a six orders of
magnitudes improvement over previous three-dimensional calculations. All the
relevant atomic and molecular cooling and heating processes, including cooling
by collision-induced continuum emission, are implemented. For calculating
optically thick H2 cooling at high densities, we use the Sobolev method. To
examine possible gas fragmentation owing to thermal instability, we compute
explicitly the growth rate of isobaric perturbations. We show that the cloud
core does not fragment in either the low-density or high-density regimes. We
also show that the core remains stable against gravitational deformation and
fragmentation. We obtain an accurate gas mass accretion rate within a 10 Msun
innermost region around the protostar. The protostar is accreting the
surrounding hot gas at a rate of 0.001-0.01 Msun/yr. From these findings we
conclude that primordial stars formed in early minihalos are massive. We carry
out proto-stellar evolution calculations using the obtained accretion rate. The
resulting mass of the first star is M_ZAMS = 60-100 Msun, with the exact mass
dependent on the actual accretion rate.Comment: 27 pages, 13 embedded figures. Revised versio
Type Ia Supernovae: Influence of the Initial Composition on the Nucleosynthesis, Light Curves, Spectra and Consequences for the Determination of Omega_M & Lambda
The influence of the initial composition of the exploding white dwarf on the
nucleosynthesis, light curves and spectra of Type Ia supernovae has been
studied in order to evaluate the size of evolutionary effects on cosmological
time scales, how the effects can be recognized and how one may be able to
correct for them.
The calculations are based on a set of delayed detonation models which give a
good account of the optical and infrared light curves and of the spectral
evolution. The explosions and light curves are calculated using a one-
dimensional Lagrangian radiation-hydro code including a nuclear network. NLTE-
spectra are computed for various epochs using the structure resulting from the
light curve code.
The following questions are addressed : What do we learn about the progenitor
evolution and its metallicity? What are the systematic effects for the
determination of the cosmological parameters and and how
can we recognize this potential 'pitfalls' and correct for evolutionary
effects?Comment: 19 pages, TeX, Ap
Mass-loss rates of Very Massive Stars
We discuss the basic physics of hot-star winds and we provide mass-loss rates
for (very) massive stars. Whilst the emphasis is on theoretical concepts and
line-force modelling, we also discuss the current state of observations and
empirical modelling, and address the issue of wind clumping.Comment: 36 pages, 15 figures, Book Chapter in "Very Massive Stars in the
Local Universe", Springer, Ed. Jorick S. Vin
GRB 021004: Tomography of a gamma-ray burst progenitor and its host galaxy
We analyse the distribution of matter around the progenitor star of gamma-ray
burst GRB 021004 as well as the properties of its host galaxy with
high-resolution echelle as well as near-infrared spectroscopy. Observations
were taken by the 8.2m Very Large Telescope with the Ultraviolet and Visual
Echelle spectrograph (UVES) and the Infrared Spectrometer And Array Camera
(ISAAC) between 10 and 14 hours after the onset of the event. We report the
first detection of emission lines from a GRB host galaxy in the near-infrared,
detecting H-alpha and the [O III] doublet. These allow an independent
measurement of the systemic redshift (z = 2.3304 +/- 0.0005) which is not
contaminated by absorption as the Ly-alpha line is, and the deduction of
properties of the host galaxy. From the visual echelle spectroscopy, we find
several absorption line groups spanning a range of about 3,000 km/s in velocity
relative to the redshift of the host galaxy. The absorption profiles are very
complex with both velocity-broadened components extending over several 100 km/s
and narrow lines with velocity widths of only 20 km/s. By analogy with QSO
absorption line studies, the relative velocities,widths, and degrees of
ionization of the lines ("line-locking", "ionization--velocity correlation")
show that the progenitor had both an extremely strong radiation field and
several distinct mass loss phases (winds). These results are consistent with
GRB progenitors being massive stars, such as Luminous Blue Variables (LBVs) or
Wolf--Rayet stars, providing a detailed picture of the spatial and velocity
structure of the GRB progenitor star at the time of explosion. The host galaxy
is a prolific star-forming galaxy with a SFR of about 40 solar masses per year.Comment: 11 pages, 5 figures. Accepted for publication in Astronomy and
Astrophysics
Group B <em>Streptococcus </em>engages an inhibitory siglec through sialic acid mimicry to blunt innate immune and inflammatory responses <em>in vivo</em>
Group B Streptococcus (GBS) is a common agent of bacterial sepsis and meningitis in newborns. The GBS surface capsule contains sialic acids (Sia) that engage Sia-binding immunoglobulin-like lectins (Siglecs) on leukocytes. Here we use mice lacking Siglec-E, an inhibitory Siglec of myelomonocytic cells, to study the significance of GBS Siglec engagement during in vivo infection. We found GBS bound to Siglec-E in a Sia-specific fashion to blunt NF-κB and MAPK activation. As a consequence, Siglec-E-deficient macrophages had enhanced pro-inflammatory cytokine secretion, phagocytosis and bactericidal activity against the pathogen. Following pulmonary or low-dose intravenous GBS challenge, Siglec-E KO mice produced more pro-inflammatory cytokines and exhibited reduced GBS invasion of the central nervous system. In contrast, upon high dose lethal challenges, cytokine storm in Siglec-E KO mice was associated with accelerated mortality. We conclude that GBS Sia mimicry influences host innate immune and inflammatory responses in vivo through engagement of an inhibitory Siglec, with the ultimate outcome of the host response varying depending upon the site, stage and magnitude of infection
Targeting of PI3K/AKT/mTOR pathway to inhibit T cell activation and prevent graft-versus-host disease development
Producción CientíficaBackground: Graft-versus-host disease (GvHD) remains the major obstacle to successful allogeneic hematopoietic stem cell transplantation, despite of the immunosuppressive regimens administered to control T cell alloreactivity. PI3K/AKT/mTOR pathway is crucial in T cell activation and function and, therefore, represents an attractive therapeutic target to prevent GvHD development. Recently, numerous PI3K inhibitors have been developed for cancer therapy. However, few studies have explored their immunosuppressive effect. Methods: The effects of a selective PI3K inhibitor (BKM120) and a dual PI3K/mTOR inhibitor (BEZ235) on human T cell proliferation, expression of activation-related molecules, and phosphorylation of PI3K/AKT/mTOR pathway proteins were analyzed. Besides, the ability of BEZ235 to prevent GvHD development in mice was evaluated. Results: Simultaneous inhibition of PI3K and mTOR was efficient at lower concentrations than PI3K specific targeting. Importantly, BEZ235 prevented naïve T cell activation and induced tolerance of alloreactive T cells, while maintaining an adequate response against cytomegalovirus, more efficiently than BKM120. Finally, BEZ235 treatment significantly
improved the survival and decreased the GvHD development in mice. Conclusions: These results support the use of PI3K inhibitors to control T cell responses and show the potential utility of the dual PI3K/mTOR inhibitor BEZ235 in GvHD prophylaxis.Asociación Española Contra el Cáncer (Proyecto AIOA110296BLAN).Gerencia Regional de Salud de Castilla y León (Proyecto GRS 726/A13
The First Decade of Science with Chandra and XMM-Newton
NASA's Chandra X-ray Observatory and ESA's XMM-Newton made their first
observations one decade ago. The unprecedented and complementary capabilities
of these observatories to detect, image, and measure the energy of cosmic
X-rays, achieved less than 50 years after the first detection of an extra-solar
X-ray source, represent an increase in sensitivity comparable in going from
naked-eye observations to the most powerful optical telescopes over the past
400 years! In this review, we highlight some of the many discoveries made by
Chandra and XMM-Newton that have transformed 21st century astronomy and briefly
discuss prospects for future research.Comment: 8 pages, 10 figures, published in Natur
Track E Implementation Science, Health Systems and Economics
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138412/1/jia218443.pd
Is diet partly responsible for differences in COVID-19 death rates between and within countries?
Correction: Volume: 10 Issue: 1 Article Number: 44 DOI: 10.1186/s13601-020-00351-w Published: OCT 26 2020Reported COVID-19 deaths in Germany are relatively low as compared to many European countries. Among the several explanations proposed, an early and large testing of the population was put forward. Most current debates on COVID-19 focus on the differences among countries, but little attention has been given to regional differences and diet. The low-death rate European countries (e.g. Austria, Baltic States, Czech Republic, Finland, Norway, Poland, Slovakia) have used different quarantine and/or confinement times and methods and none have performed as many early tests as Germany. Among other factors that may be significant are the dietary habits. It seems that some foods largely used in these countries may reduce angiotensin-converting enzyme activity or are anti-oxidants. Among the many possible areas of research, it might be important to understand diet and angiotensin-converting enzyme-2 (ACE2) levels in populations with different COVID-19 death rates since dietary interventions may be of great benefit.Peer reviewe
Incident type 2 diabetes attributable to suboptimal diet in 184 countries
The global burden of diet-attributable type 2 diabetes (T2D) is not well established. This risk assessment model estimated T2D incidence among adults attributable to direct and body weight-mediated effects of 11 dietary factors in 184 countries in 1990 and 2018. In 2018, suboptimal intake of these dietary factors was estimated to be attributable to 14.1 million (95% uncertainty interval (UI), 13.814.4 million) incident T2D cases, representing 70.3% (68.871.8%) of new cases globally. Largest T2D burdens were attributable to insufficient whole-grain intake (26.1% (25.027.1%)), excess refined rice and wheat intake (24.6% (22.327.2%)) and excess processed meat intake (20.3% (18.323.5%)). Across regions, highest proportional burdens were in central and eastern Europe and central Asia (85.6% (83.487.7%)) and Latin America and the Caribbean (81.8% (80.183.4%)); and lowest proportional burdens were in South Asia (55.4% (52.160.7%)). Proportions of diet-attributable T2D were generally larger in men than in women and were inversely correlated with age. Diet-attributable T2D was generally larger among urban versus rural residents and higher versus lower educated individuals, except in high-income countries, central and eastern Europe and central Asia, where burdens were larger in rural residents and in lower educated individuals. Compared with 1990, global diet-attributable T2D increased by 2.6 absolute percentage points (8.6 million more cases) in 2018, with variation in these trends by world region and dietary factor. These findings inform nutritional priorities and clinical and public health planning to improve dietary quality and reduce T2D globally. (c) 2023, The Author(s)
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